The present invention relates to a guide device for the guidance of a load carrier of an elevator installation along at least one guide surface.
By the term ‘load carrier’ there are to be understood in this connection all movable masses which can be moved in an elevator installation along a guide surface. Falling under this term are, in particular, elevator cars and counterweights. The latter serve in an elevator installation for compensation for the weight of other load carriers.
A guide device of the stated kind is used in elevator systems in order to stabilize the position of a load carrier movable along a guide surface. Such a guide device usually comprises at least one guide element which is disposed in contact with the guide surface and is connected with the load carrier by means of a connecting element in such a manner that the guide element is movable relative to the load carrier or the load carrier is movable relative to the guide element.
In a typical realization of the guide device, the respective guide surface can be defined by, for example, the surface of a guide rail and a roller can be used in each instance as a guide element and a resiliently deformable structure, which connects a rotational axle of the roller with the respective load carrier, in each instance as a connecting element. The connecting element can be, for example, a spring or an arrangement of several springs. In addition, several guide surfaces and correspondingly several guide elements can be used for guidance of the respective load carrier.
Connecting elements which allow a resilient deformation in the case of a mechanical load offer the possibility of connecting a guide element with a load carrier in such a manner, and in each instance keeping it in contact with a guide surface, such that the respective connecting element is deformed to a predetermined extent by comparison with a relaxed state and thus has a predetermined bias. By virtue of the bias, each guide element exerts a force on the respective guide surface. Such connecting elements are used in order to stabilize the load carrier in its equilibrium position with respect to the guide surface. If the respective connecting element is deformed in the case of deflection of the load carrier out of the equilibrium position, then there results therefrom a restoring force which acts on the load carrier and the size of which grows with increasing deflection of the load carrier out of the equilibrium position and thus opposes the deflection. It is thus ensured that the load carrier adopts an equilibrium position with respect to the respective guide surface when the guide element is constantly in contact with the respective guide surface.
The respective connecting element substantially determines the travel behavior of a load carrier moved along a guide surface. The stiffness of the connecting element is of particular significance in that case. The stiffness of the connecting element is a measure for a change in the force which has to be realized in order to change the position of the respective guide element by a predetermined distance.
The stiffness of a connecting element plays a significant role with respect to the travel comfort particularly in the case of a guide device for guidance of an elevator car. The connecting elements have to be so constructed in every case that they absorb the maximum permissible disturbance forces and keep a deviation of the load carrier from a predetermined equilibrium position within a predetermined limit. Different requirements have to be taken into consideration in the design of a connecting element with respect to stiffness. If the stiffness is too great, the elevator car has a hard coupling to the respective guide surface by way of a connecting element and the corresponding guide element. In this case during travel of the elevator car disturbing forces due to non-rectilinearities of a guide surface or load displacements lead to severe shocks which would be perceived by passengers to be unacceptable. If—at the other extreme—the stiffness is too low, then small deflections of the elevator car from the equilibrium position would indeed be sensed by passengers as less disturbing. On the other hand, large disturbing forces would lead to unacceptably large deflections of the elevator car from the equilibrium position. The latter is problematic, since only a limited space is available for lateral deflections of a elevator car perpendicularly to its direction of movement and, in addition, the connecting elements for constructional reasons—in order to avoid a mechanical contact between stationary and moved components of the elevator installation and damage of individual parts—allow only a limited play for relative movement of a guide element with respect to the elevator car. For example, the movement of the elevator car relative to a guide device is limited by the construction of a safety brake device, which the elevator car has to have in order to brake the elevator car at guide surfaces of the guide rail in the case of emergency and to stop it. During normal travel the elevator car may, in fact, deflect only so far from an equilibrium position with respect to the guide surfaces that the safety brake device does not come into contact with the guide surfaces.
Known connecting elements which act by a single spring on a guide element have a stiffness which is intrinsic to construction and which is usually constant for all positions of the guide element. With a connecting element which has a constant stiffness, however, the requirements which have to be fulfilled in operation of an elevator installation cannot be fulfilled or are able to be fulfilled only insufficiently. In the best cases, compromise solutions are possible which are unsatisfactory with respect to usual expectations, particularly with respect to the extreme requirements imposed in the case of applications in high-speed elevators.
With the speeds at which high-speed elevators are operated even slight unevennesses of guide surfaces lead to large transverse forces. In order to ensure, in operation, an acceptable travel comfort even in the case of large transverse forces, guide devices were proposed with a respective connecting element having a stiffness which is variable in dependence on the setting of the guide element relative to the respective load carrier.
For example, there is shown in European patent EP 0 033 184 a guide device for a load carrier of an elevator installation in which at least one guide element is disposed in contact with the guide surface and is connected by means of a connecting element with the load carrier in such a manner that the guide element is movable relative to the load carrier between different positions in a first and a second positional range. The connecting element comprises a first and a second resilient element in the form of a first and a second helical spring. The helical springs are arranged in series in such a manner that in the case of movement of the guide element in the first positional range the two helical springs are deformed in the direction of their longitudinal extent. A change in length of the first helical spring is mechanically limited in such a manner that in the case of movement of the guide element in the second positional range exclusively the second resilient element is deformed. The two helical springs each have a constant stiffness, wherein the stiffness of the second helical spring is greater than the stiffness of the first helical spring. This results in an overall stiffness of the connecting element which is determined by the respective stiffnesses of the first and second helical springs and is a function of the respective position of the guide element. The overall stiffness adopts higher values in the second positional range than in the first positional range. In this construction of the connecting element the overall stiffness of the connecting element is constant each time not only in the first positional range, but also in the second positional range. With this construction of the connecting element it is indeed possible, through appropriate specifications for the stiffnesses of the first and the second helical spring, to softly couple the guide element to the guide surface when the guide element is disposed in the first positional range and to firmly couple it to the guide surface when the guide element is disposed in the second positional range. However, in the case of transition of the guide element from the first positional range to the second positional range an abrupt transition from soft to hard coupling to the guide surface takes place. The overall stiffness of the connecting element accordingly has a non-constant jump at the transition of the guide element between the first positional range and the second positional range. This abrupt transition is in operation more disturbing the greater the difference between the stiffnesses of the two helical springs. Since each connecting element accepts the maximum permissible disturbing forces and has to keep deviation of the load carrier from a predetermined equilibrium position within a predetermined limit, the stiffness of the second helical spring must be selected to be greater the smaller the stiffness of the first helical spring. Accordingly, an improved travel comfort in the case of small deflections of the load carrier from its equilibrium position is achieved and in that case a diminished travel comfort in the region of the transition between the first and the second positional range is taken into account.